Electrical resistance and method of making same



E. R. STOEKLE June 24, 1930.

ELECTRICAL RESISTANCE AND METHOD OF MAKING SAME Filed June 2'7, 1927 2 Sheets-Sheet l INVENTOR. MK M M W4 MW ATTORNEY.

June 24, 1930. E. R. STOEKLE 1,767,716

ELECTRICAL RESISTANCE AND METHOD OF MAKING SAME Filed June 2'7, 192'? 2 Sheets-Singet 2 INVENTOR. 5 A? M BY M M ATTORNEY.

- Patented June 24, 1930 sop .ties and impracticability UNITED STATES PATENT OFFICE ERWIN R. STOEKLE, OF MILWAUKEE, WISCONSIN, ASSIGNOR '10 CENTRAL RADIO LABORATORIES, OF MILWAUKEE, WISCONSIN, A CORPORATION OF WISCONSIN ELECTRICAL RESISTANCE AND mnrnoii oi" MAKING SAME Application fi led June 27,

This invention relates to improvements in electrical resistances and in the methods of making the same.

One object is to provide a resistance occupying a minimum of space for the required resistance.

Another object is to provide a resistance in which the area enclosed by each turn of the resistor wire shall be a minimum resulting in a minimum of self induction.

Another object is to provide a very thin, flat resistance element wound on a heat resistant flexible sheet which may be formed into any desired shape suitable for a,com pact fixed resistance-0r for the resistor of a rheostat. Y

Another object is to provide an improved method of making resistances of the above described character which method consists of winding the resistor in the form of a cylindrical helix and subsequently forming it into the desired flat shape. The difiiculof winding a wire helix on a thin, wide, flat strip are well known and are due principally to the nonuniform tension in the wire while it is being wound, resulting in breakage of the wire and requiring very slow winding speeds. In the method herein disclosed, the high speed of winding, which is entirely practical when winding a cylindrical helix, is used and by simple operations the cylindrical helix is transformed into a thin, flat, wire-wound flexible strip. The thin, flat, wire-wound strip thus produced is adapted to be and in some embodiments of the invention is rolled or curved, or is first folded and then curved or suitably shaped for assembly in a rheostat or other form of variable resistance.

Other objects and advantages reside in the novel features of. the method and in the construction, arrangement and combination of the parts of the resistor as will be hereinafter more fully described and particularly pointed out in the appended claims, reference being had to the accompanying drawings forming apart of this application, and in which: i. I

Figure 1 is a view in perspective illus- 1927. Serial No. 201,926.

trating diagrammatically the first step of the method;

Figure 2 is a similar View illustrating the step of collapsing or flattening the wirewound tube by pressure;

Figure 3 is a plan view showing one form of resistor;

Figure 4 is a perspective view illustrating the operation of folding a flat resistor;

Figure 5 is a perspective view showing the folded resistor in final form;

Figure 6 is a similar view showing a rolled form of resistor;

Figure 7 is a fragmentary sectional view taken-in the plane of line 77 of Figure 8;

Figure 8 is a view in lon itudinal diametrical section showing the Folded resistor embodied in a variable resistance, parts bemg shown in elevation for the sake of illustration; and

Figure 9 is a fra entar ers e ctive view showing the st iiture of Figure 8 adapted for use as a potentiometer.

As shown in Figure 1, a thin walled tube 1, preferably made of asbestos paper, is wound with a helix of wire 2. As the wire 2 s wound" on a cylinder, high speed winding is employed without breakage during the wlnding operation. During the winding operation the tube is mounted on a collapsible mandrel M as illustrated diagrammatically in Figure 1, the mandrel being removed following the winding operation. The tube 1 and helix 2 are next coated or dipped in a suitable adhesive cement or heat resistant glue which not only serves to fasten the wiresto the tube but also insures insulation .of ad acent turns from each other as it possesses electrical insulating properties. The interior of the tube is also coated with adhesive to cause the inner surfaces of the tube to adhere to each other after pressing. The

'tube is then placed between parallel flat allowed to harden. In order to assist the hardening of the adhesive used in the structure, it is preferable to bake the finished unit at a suitable temperature.

One convenient form of a finished fixed resistance comprises the above described fiattened strip which is, in its final form, as shown in Figure 8, provided with suitable insulated mounting eyelets 5 and 6. The soldered terminals 7 and 8 are in electrical contact with the ends of the wire helix and are securely riveted to the strip 1 or fastened thereto by eyelets or the like. The eyelets 5 and 6 are adapted to coact with mounting screws or the like by which the resistor may be fastened to any desired support.

Another form of resistor is shown in the Figures 1 and 5. As shown in Figure 4,

the strip 1, after the completion of the flattening operation illustrated in Figure 2, and before complete hardening or setting, is

folded through the center transverse to the wires of the helix, that is, along the longitudinal median line of the strip. An insulating sheet 9, preferably of asbestos paper coated with adhesive, is inserted between the adjacent surfaces of the folded strip in order to prevent contact between the wires of the helix. This folded strip is then pressed into the flat form shown in Figure 5 and the insulating sheet 9 is trimmed down if and as may be necessary. Suitable mounting eyelets 10 and 11 are provided and are insulated from the resistor as before. Terminal lugs 12 and 13 are fastened to the strip with rivets or eyelets and serve to establish electrical connection with the ends of the wire helix. Here again, in order to harden the adhesive and thus give the finished resistance greater rigidity, it has been found desirable to bake the finished unit at a suitable temperature.

A still further compact form of the fixed resistor is shown in Figure 6. In this form, the resistor, after being completely flattened in the manner shown in Figure 2 but before complete hardening or setting, is rolled into a cylinder. Before rolling, an insulating sheet, preferably of asbestos paper, is pasted with adhesive to the fiat wire-wound strip in order to insulate the wire on adjacent convolutions of the rolled cylinder. This sheet between the convolutions is shown at 14 in Figure 6. Metal rings or caps 15 and 16 are pressed over the ends of the cylindrical unit and serve as terminals to establish electrical connections to the ends of the wire.

Another way in which insulation of the wires of the helix may be accomplished is b pasting a thin, insulating sheet, preferably of asbestos, over the cylindrical helix shown in Figure 1. After flattening as shown in Figure 2, the resultant sheet will have the wires of the helix held between two sheets of asbestos and many then be formed into any of the above described resistors without danger of short circuiting adjacent wires. A sufficiently flexible insulating cement may also be applied over the wires of the helix in Figure 1 which will insure insulation of the wires during the subsequent forming processes.

The resistors above described are all characterized by the fact that each turn of the flattenedhelix encloses a small area thus minimizing the self induction of the unit. In the folded resistors such as shown in Figures 4 and 5, there is a further decrease in selfinduction because of the fact that the magnetic field due to the current in the wires on the inner folded surface is opposite to the magnetic field created by the wire elements on the outer surface. Resistor strips only y" thick, 1 inches wide and 5 lon have been constructed with a resistance 0 20,000 ohms. A low value of self induction is desirable when such high resistances are used in radio circuits, and the construction of the above described resistances is, therefore, particularly advantageous for radio applications.

Figures 7, 8 and 9 show the application of a folded resistor similar to that of Figure 5, to the construction of a variable resistance such as a rheostat and potentiometer.

In both of these adaptations of the invention, a cylindrical cup 18 receives and retains the folded resistor 17 which is of split annular form and which is insulated from the cup 18 by an insulting sheet 19 and an insulating washer 20 (Figure 8). A threaded bushing 23 is shouldered as at 23 and is fastened to the cup 18 by a nut 24 which clamps the shoulder 23 against the base of the cup, the nut 24 also being cooperable with a nut 25 to mount the rheostat on a panel. A shaft 26 is rotatably fitted in the bushing 23 and carries at one end an operating knob 27 and at its other end a contact shoe 28 which makes a sliding contact with the wires on the folded edge of the resistor 17. By having the contact shoe 28 of the angular form shown it is possible to terminate the shaft 26 and bushmg 23 within the resistor to protect the same and to make the device more compact,

It is to be understood that when the variable resistance, just described, is employed as a rheostat one arrangement of binding posts will be employed whereas when the variable resistance is adapted for use as a potentiometer then a somewhat different binding post arrangement is provided.

When used as a rheostat the bindin post arrangement of Figure 7 is employe and, as shown, comprises the binding post 21 insulated from the cup 18 b means of a fiber bushing and washer 21 an electrically connected to one end of the folded wire helix of the resistor. A second binding post 22 is provided and is fastened to the cup 18 in such manner as to be electrically connected therewith.

electromotive force applied at the terminals 21 and 22 will cause a current to flow from 21 through the wire of the resistor to the point of contact of shoe 28 with the wire, through the shoe,

shaft 26, bushing 23, and cup 18 to the other terminal 22.

When employed as a potentiometer terminals 30 and 31 are fixed to the ends of the folded wire helix of the resistor in direct and immediate electrical contact therewith. In between the ends of the split of the folded and curved resistor 17 a third terminal 32' is provided and is fixed to the cup 18 in electrical connection therewith and consequently in electrical connection with the contact shoe 28. In accordance with the usual practice, when the. variable resistance is used as a potentiometer an electromotive force is applied to the terminals 30 and 31 and is impressed after the desired modification by the resistor 17 upon a circuit electrically connected with the terminal 32 and one or the other of the terminals 30 or 31.

The folded resistor allows twice the amount of resistance to be obtained in about the same space as would be occupied by a sim le wound strip such as is commoniy use in small rheostats of this character. t also ives a resistor of smaller self induction for t e same resistance because of the thinness of the helix and its configuration. The thinness and flexibility of the flattened resistor strip allows it to be readily folded and formed into a ring required in the rheostat of Figures 7 and 8. The adhesive used for holding the wires in place and for holding together the adjacent surfaces of the flattened and folded strip ma be of such a nature as to become quite ard on baking and thus the resistor will maintain its form after the baking process.

Other advantages of this improved resistor and method of making the same Wlll be apparent to those skilled in the art and other convenient configurationsof the thin wire-wound sheet will be ada ted tovarious applications. For example t e wire-wound sheet may be rolled into a cylinder having its axis parallel to the wire elements of the helix instead of transverse as shown in Figure 6.

By formin the core of a flattened tube, the core *iso a two-ply construction in its final form with the edges of the plies joined. This provides rounded edges which prevent abrupt bending in the wirewinding thereby tending to prevent breakage of the wire and also causing the turns along the edges to be better adapted for coaction with the contact shoe.

The invention claimed is:

1. The method of making electrical resistances which comprises winding a wire helix on a collapsible tube, coating said helix and tube with a suitable insulating adhesive, pressing said helix and tube into a flattened' sheet, forming said sheet into a convenient form, and subjecting said formed sheet to heat to harden said adhesive whereby a resistor of desired form having a minimum of self induction compared to its resistance may be obtained.

2. The method of making electrical resistances which comprises winding a wire helix on a thin walled tube supported by a collapsible mandril, removing said mandril, coating said helix and tube with adhesive cement, and pressing said tube and helix into a thin flat strip. 3. The method of making an electrical resistance which comprises winding a Wire helix 'on a tube having thin flexible walls, supported by a suitable collapsible mandril, removing said tube from said mandril, coating the outside and inside surfaces of said tube with a suitable adhesive, and pressing said tube and helix into a thin flat sheet.

4. The method of making an electrical resistance which comprises winding a wire helix on a tube having thin flexible walls, supported by a suitable collapsible mandril, removing said tube from said mandril, coating the outside and inside surfaces of said tube with a suitable adhesive, pressing said tube and helix into a thin flat sheet, suitably shaping the flat sheet so' formed and then effecting hardening .thereof whereby the adhesive 'maintains the resistance in itsfinal form.

5. The method of making electrical resistances which comprises winding a wire helix on an asbestos paper tube, coating said helix and tube with a heat resistant and insulating adhesive and collapsing said tube and helix under pressure into a thin flat sheet.

6. The method of making electrical resistances which comprises winding. a wire helix on a thin walled tube supported by a collapsible mandril, removing said mandril,

transverse to the wires of said flattened helix iii order to obtain a resistor of maxi-1 mum resistance having a minimum of self induction and occupying a minimum of space.

8. The method of making electrical resistances which comprises winding a wire helix on a tube having thin flexible walls, coating said helix and tube with a suitable insulating adhesive, pressing said helix and tube into a flattened sheet, rolling said strip transverse to the wires of said flattened helix to form a cylindrical resistor of maximum resistance and minimum self induction occupying a minimum of space.

9. The method of making electrical resistances which comprises winding a wire helix on a tube having thin flexible walls, coating said helix and tube with a suitable insulating adhesive, pressing said helix and tube into a flattened sheet, folding said sheet transverse to the wire of said flattened helix. and forming said folded strip and helix into a ring or other form suitable for mount ing in a rheostat.

10. The method of making an electrical resistance which comprises winding a wire helix on a tube having thin flexible walls, supported by a suitable collapsible mandril; coating said helix and wire with an adhesive; pasting a thin insulating sheet over said helix; removing said tube from said mandril; coating the inner surfaces of said tube with adhesive, pressing said tube and covered helix into a thin flat sheet, folding or rolling said sheet into a compact form to make a resistance occupying a minimum of space and having a minimum of self induction.

11. The method of making an electrical resistance which comprises winding a wire helix on a tube having thin flexible walls, supported by a suitable collapsible mandril; removing said tube from said mandril; coatin the outside and inside surfaces of said tu e with a suitable adhesive; pressing said tube and helix into a thin flat sheet, folding said sheet transverse to the wires, inserting an insulating sheet between the folded surfaces of said wire-wound sheet, pressing said I folded sheet into a compact strip, and forming said strip into a ring to form the resistance element of a rheostat.

12. A resistance of the character described comprising a flat strip-like core made up of a plurality of plies of insulating material with the adjacent edges of the plies joined to provide somewhat rounded edges along and adhesive insulating material for ,securing said portions and for holding said insulation in folded position.

14. In combination, a strip of insulation having resistance wire wound transversely thereon, said strip being folded longitudinally to position portions of each turn of wire adjacent one another to provide a compact non-inductive resistance unit.

15. The method of making electrical resistances which comprises winding a wire helix on a thin walled tube supported by a collapsible mandrel, removing said mandrel, applying adhesive material'to the inner wall of the tube, and pressing said tube and said helix into a thin flat strip.

In witness whereof, I hereto afiix my signature.

ERWIN R. STOEKLE.

the core and a winding of wire on said core and passing over said edges, said core with the windings thereon being folded whereby portions of the windings are closel associated to render the resistance non-in uctive.

13. A resistance unit including a strip of insulation having resistance material positioned on o posite surfaces thereof, said. stri being olded to position portions of sai resistance material adjacent each other 

